The influence of a vibrating upper lip on the sound generation in flue organ pipes - A combined experimental/numerical study

Conference poster, 2007

A combined experimental/numerical study investigating the relation between vibrations of the upper lip and the acoustical energy accumulated inside a flue organ pipe resonator will be presented. A characteristic flue organ pipe was mechanically excited at the upper labium. Input force, surface velocities of the pipe walls and sound pressure inside the pipe were measured for this load case. The measurements assumed steady state conditions, i.e. the pipe was driven using broadband noise and signal analysis was performed in the frequency domain. The experiment was then simulated using a finite element approach. Generally, due to uncertainties in material and geometrical data, modelling a crafted instrument is not easy. However, in the low frequency range numerical results matched well the experimental data. This allowed using the model to identify the energy flow from the excitation point to positions where the sound pressure was picked up with the microphone. Results indicate that an overly yielding labium can indeed have a strong influence on the sound generation. It will also be shown that in general this will not be desired, since the degree of coupling between sound field and vibrating labium is very sensitive to material and structural properties, i.e. hard to control.